A modern refrigerator is a complex unit where each element plays a role in maintaining food freshness. The heart of the climate control system is thermal sensorwhich continuously monitors temperature changes inside the chambers. It is on its correct operation that it depends whether the meat will not defrost and whether the vegetables will not freeze in the “zero” zone.
Many users notice the strange behavior of the equipment: the compressor hums without stopping or, conversely, is silent for hours, allowing food to spoil. Often the reason lies in the failure of the sensor readings. In this article we will analyze in detail what this element is, what types exist and how to understand that it has failed.
The principle of operation and the main types of sensors
The operation of any temperature sensor is based on the physical property of materials to change their characteristics under the influence of heat. In refrigeration technology, there are most often two main types of elements: thermoresistors and thermostats mechanical type. Understanding the difference between them is critically important when diagnosing.
Thermostats operate on the principle of expansion of a gas or liquid in a sealed flask. When the temperature rises, the substance expands and opens the contacts, turning off the compressor. It's a reliable but rough mechanic. In contrast, thermistors (NTC-type) are electronic components whose resistance drops when heated. They transmit precise digital data to control module.
Electronic systems allow you to maintain the temperature with an accuracy of a degree, while mechanical systems allow fluctuations of 3-5 degrees. Modern models, such as LG or Samsung, use a whole network of 5-8 sensors in different zones.
Why are electronics more sensitive?
Mechanical thermostats have hysteresis - a response delay. Electronic thermistors respond to changes instantly, which allows inverter compressors to operate in an economical mode without turning on at full power.
The location of the elements in different models
Where exactly to look for the sensor depends on the design of your refrigerator. In classic single-compartment models, the evaporator is usually located behind the back wall of the freezer. The main sensor is installed here, which controls the defrosting and cooling cycle.
In systems No Frost the situation is more complicated. Sensors can be installed:
- 🌡️ On the evaporator - to control the freon temperature and start defrosting.
- ❄️ In the air duct - to measure the temperature of the blown air.
- 🥩 In the freshness zone - separate sensors for “zero” cameras.
- 🧊 On the case - to protect against compressor overheating.
Access to them is often limited by plastic panels. For example, in refrigerators Bosch the main sensor can be hidden under a decorative cover on the ceiling of the chamber. Before starting any work, it is necessary to turn off the power to the device and carefully dismantle the lining so as not to damage the fragile plastic clips.
⚠️ Attention: When removing plastic panels in the freezer, be extremely careful. Plastic becomes brittle in the cold and can burst from careless movement even with careful handling.
Symptoms of a faulty temperature sensor
How can you tell that it is the temperature sensor that has failed and not the compressor or thermostat? There are a number of characteristic signs, ignoring which can lead to expensive repairs of the entire unit.
The first and most obvious symptom is continuous operation of the compressor. If the refrigerator hums without interruption, but the temperature inside does not drop to the set values, or, conversely, the food in the freezer turns into an icy monolith, this is a sure sign that the sensor is “lying” to the controller.
The second symptom is frequent turning on and off of the motor. This phenomenon is called "clocking". The electronics receive conflicting signals and try to compensate for differences, wearing out the starting relay.
The third sign is relevant for No Frost systems. If a “coat” of ice builds up on the evaporator, although the sensor is visually intact, it may not give the command to turn on Defrost heating element. As a result, the channels become clogged with ice, and cold stops flowing into the main chamber.
Diagnostics and testing with a multimeter
For accurate diagnosis, you will need a digital multimeter. A visual inspection rarely gives results, since a break inside the housing or a change in resistance is not visible to the eye. The test is carried out in resistance measurement mode (Ohm).
The test process is as follows:
- Disconnect the sensor connector from the control board.
- Connect the multimeter probes to the sensor contacts.
- Record the readings at room temperature.
- Place the sensor in a glass of water of known temperature (you can use a thermometer for control).
- Compare changes in resistance with the reference table.
For a working thermistor, the resistance should change smoothly as the water temperature changes. If the device shows infinity (open) or zero (short circuit) regardless of the conditions, the element is faulty.
| Sensor type | Resistance at +25°C | Resistance at -18°C | Acceptable error |
|---|---|---|---|
| NTC 5 kOhm | ~5000 Ohm | ~25000 Ohm | ±5% |
| NTC 10 kOhm | ~10000 Ohm | ~45000 Ohm | ±3% |
| PTC (rarely) | Increases with heating | Falls with cooling | ±10% |
Instructions for replacing the temperature sensor
Replacing the temperature sensor is a procedure that can be done with your own hands, if you follow safety precautions and the sequence of actions. The main rule: all work is carried out only on completely de-energized equipment.
First you need to get to the installation site. In a freezer, it is often necessary to defrost the unit for 10-12 hours to remove the back panel to gain access to the evaporator. Then the old element is carefully disconnected.
The new sensor is installed in the same location. It is important to ensure firm contact with the surface it is to control. Often used thermal conductive grease or a special clamp to improve heat transfer.
☑️ Algorithm for replacing the sensor
After assembling and turning on the refrigerator, do not expect an instant result. The electronic control unit may take time (from 30 minutes to several hours) to analyze the new readings and enter operating mode.
⚠️ Attention: Never use regular glue or electrical tape to secure the sensor to the metal evaporator tube. This will disrupt heat transfer, and the sensor will show the wrong temperature, which will lead to malfunctions.
Configuration and calibration after replacement
In most cases, replacing the sensor does not require complex software settings - the system itself calculates the new parameters. However, in some premium models, you may need to enter service menu to reset errors.
A combination of buttons is often used to enter the service mode. For example, simultaneously pressing the “Defrost” and “Temperature” buttons for 5–10 seconds. The interface may differ depending on the brand: Samsung, LG or Whirlpool use different algorithms.
If after replacement the refrigerator continues to work incorrectly, check the integrity of the wires going from the sensor to the board. Often a fracture occurs at the very entrance to the housing or at the bend of the door.
What to do if there is no original sensor?
You can use a universal analogue with a similar resistance rating. However, it is important to consider that the resistance curve may differ, which will lead to a slight error in maintaining the temperature.
Is it possible to temporarily short-circuit the sensor to make the refrigerator work?
Technically, this is possible for some models, where the short circuit simulates strong cooling, forcing the compressor to work constantly. However, this dangerous measure: the refrigerator will not turn off, the evaporator will be covered with ice, and the compressor will burn out from overheating in a short time. Use only for emergency defrosting under supervision.
Why doesn’t the new sensor solve the problem?
There may be several reasons: oxidized contacts in the connector, a malfunction of the control board itself, which does not process signals correctly, or a problem in the refrigerant circulation system. It is also possible that a sensor with an inappropriate resistance rating is installed.
How often should you change a temperature sensor?
The service life of a high-quality thermistor is 7–10 years or more. It is not a consumable item and is replaced only in case of (malfunction). Preventative replacement is not required.